A door is provided with a door closer for surely closing the door. And in the case of either a building, such as a condominium building, that is made substantially airtight or a large door, a large force is required for opening a door, which imposes a large burden on children and the elderly. Therefore, a door-opening-assistance device is used to assist in opening a door in such a situation.
A conventional door-opening-assistance device is a member that is separate from a door closer, and it has a structure such that a slider is meshed with a shaft member that, because it is connected to the rotary shaft of the door closer, rotates and moves forward and backward, and such that an energizing spring stores door-opening force in accordance with the movement of the slider. Also, such a door-opening-assistance device includes both a locking member that locks the energizing spring so that the spring stores the door-opening force, and an unlocking member that unlocks the locking member by the closing of the door, and the locking member and unlocking member are in a housing separate from the door closer.
Such a separate type of door-opening-assistance device is mounted to the door closer after the door closer is mounted to the door, and the door is provided with door-opening force that can be used to counter the door closer's door-closing force, thereby reducing the amount of force needed to open the door. Accordingly, the door can be opened by a small amount of force. Patent Document 1: Japanese Patent Application Laid-Open No. 2004-143812